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Gives the position of  the year in the Metonic cycle.  This is a 1..19
number.

This subroutine applies to both western and eastern computs.

=item * western_epact($year)

In the  Gregorian comput, the epact  is the age of  the ecclesiastical
Moon on the 1st January of the  given year. The C<western> part of the
subroutine  name  accounts for  the  fact  that Gregorian  and  Julian
calendars do not use the same formula.

The epact  is a 0..29 number.  The "0" value  is shown as "*"  in some
sources. This  subroutine does not convert  "0" to "*", the  result is
always a pure number.

Actually,  the western  epact  is  a little  more  than  a number.  As
explained by Paul Couderc (page 86)  and Jean Lefort (page 142), there
is a  special case for 25,  which should be considered  as two values,
"basic 25" and "alternate 25". "Basic 25" is printed as a plain number
C<25>, while "alternate 25" is printed  in a way that distinguishes it
from the other  numbers. Jean Lefort mentions C<XXV>  or using italics
or bold  digits, such as  B<C<25>>. This module prints  the "alternate
25" as "C<25*>".

=item * eastern_epact($year)

In the Julian comput, the epact  is the age of the ecclesiastical Moon
on 22nd March. The C<eastern> part of the subroutine name accounts for
the  fact that  Gregorian and  Julian calendars  do not  use the  same
formula.

The epact  is a 0..29 number.  The "0" value  is shown as "*"  in some
sources. This  subroutine does not convert  "0" to "*", the  result is
always a pure  number. There is no  other special case, for  25 as for
any other number.

The formula given by Reingold and  Dershowitz is a "shifted epact" and
gives  different  results from  the  values  printed in  Lefort's  and
Couderc's books. The module follows Couderc and Lefort.

=item * western_sunday_letter($year), eastern_sunday_letter($year)

On normal years (that is, excluding  leap years), the Sunday letter is
determined by tagging 1st January with  "A", 2nd January with "B", and
so on and looking at the first sunday of the year. The letter found at
this sunday if the sunday letter for the year.